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Effect of Pulmonary Consolidation on Respiratory Sounds

Abstract 2097 Poster Session IV, Tuesday, 5/4 (poster 183)

Introduction: Since ancient times clinicians have listened to changes in respiratory sounds (RS) as indicators of pulmonary consolidation. We used computerized RS analysis to study the acoustical changes associated with consolidation. Methods and subjects: We studied 5 children with lobar consolidation (A: 14y boy with blastomycosis [BM], B: 12y girl with community acquired pneumonia [CAP], C: 6y boy with CAP, D: 3y boy with BM, E: 11y boy with BM). Air flow and RS over the trachea (TRA), the consolidated lung (CSL) and the corresponding site of the contralateral lung (CON) were recorded. The sound signals were low-pass filtered at 2.5 kHz and amplified. Flow and sound data were digitized at 10 kHz per channel. Fast Fourier transformation was performed on the acoustical data. Average inspiratory and expiratory spectra were computed at flows of 15 ml/s/kg ±20% tolerance. In expiration, the signal-to-noise ratio at tracheal RS resonance peaks (p_res) was identified and compared with corresponding peaks in RS spectra over the lung. After substracting background noise from RS, the power of inspiratory and expiratory sounds at low (150-300 Hz) and high frequencies (600-1200 Hz) was calculated. The difference between CSL and CON within both frequency bonds (ΔPlow and ΔPhigh) was evaluated. Results: There was decrease in low frequency RS over CSL during inspiration (p=0.033, paired t-test) and expiration (p=0.035). High frequency RS increased (p=0.003) and P_res was significantly greater over CSL than over CON (p=0.017) but only during expiration (n/a = not available because of abundant inspiratory crackles). (Table) The RS differences decreased in magnitude in the 3 patients who had follow-up during clinical and radiographic improvement to date. Increased of high frequency sound, i.e. bronchial breathing, is well recognized in pulmonary consolidation. The reason for decreased energy at low frequencies is less well understood and requires further study. RS assessment by auscultation, with particular attention to expiration, is valuable to detect and follow pulmonary consolidation. Computerized RS analysis offers an objective quantification of changes during therapy.

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Shirota, K., Pasterkamp, H. Effect of Pulmonary Consolidation on Respiratory Sounds. Pediatr Res 45, 355 (1999).

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